Setting 'pragma_cache_size' in particular can be beneficial. It's the size of the page cache used by SQLite. See SQLite's documentation for more information.

Increasing it might speed up Hailo, especially when disk IO is slow on your machine. Obviously, you shouldn't bother with this option if 'in_memory' is enabled.

Setting 'pragma_synchronous' to 'OFF' or 'pragma_journal_mode' to 'OFF' will speed up operations at the expense of safety. Since Hailo is most likely not running as a mission-critical component this trade-off should be acceptable in most cases. If the database becomes corrupt it's easy to rebuild it by retraining from the input it was trained on to begin with. For performance reasons, these two are set to 'OFF' by default unless 'in_memory' is enabled.

When set to a true value, Hailo behaves much like MegaHAL. The entire database will be kept in memory, and only written out to disk when the save method is called and/or when the Hailo object gets destroyed (unless you disabled save_on_exit). This is disabled by default.